That is only a temporary marriage of convenience- they both hate the US for different reasons. The Chinese culture is extremely paranoid. Their trust of Russia is no deeper than their trust of the US. Their cultures are so disparate.
By the way, the Russian economy is a heck of a lot more frail than people would believe. In a way they are very much like the Middle East- dependent on oil and gas sales. Any change in technology and that economy can crash. The manufacturing base in Russia is weak. I buy from them and they are cheaper than China.